Device and method for constructing a layer body

ABSTRACT

The invention relates to a device for constructing a laminar body from a plurality of superimposed layers of free-flowing material, in particular particulate material, and a build platform within a working area. The layers are solidified in locally predetermined regions by the action of binders and are joined together so that at least one moulded body is formed by the solidified and joined regions of the layers. The device comprises a discharging device movable back and forth over the working area in at least one discharge direction and having at least one discharge opening from which the free-flowing material can be discharged in individual superimposed layers during the movement of the discharging device.

CLAIM OF PRIORITY

This application is a continuation of U.S. patent application Ser. No.14/976,586 filed on Dec. 21, 2015 and further claims priority to U.S.patent application Ser. No. 13/883,397 filed on May 3, 2103 (now U.S.Pat. No. 9,242,413), International Patent Application PCT/DE2011/001850filed on Oct. 14, 2011, and German Patent Application DE 10 2011007957.2 filed on Jan. 5, 2011, the contents of which are eachincorporated herein by reference in its entirety.

BACKGROUND INFORMATION

The invention relates to a device and a method for constructing a layerbody from a plurality of superimposed layers of free-flowing material,in particular particulate material, on a build platform within a buildspace, the layers being solidified and joined together in locallypredetermined areas by the action of a binder so that at least onemolding is formed by the solidified and joined areas of the layers, thedevice comprising a discharging device which is movable back and forthover the build space in at least one discharge direction and which hasat least one discharge opening from which the free-flowing material isdischargeable in individual superimposed layers during the movement ofthe discharging device.

A computer-controlled method for producing three-dimensional moldings isdescribed in EP 0 431 924 B1. Free-flowing particulate material isapplied in a thin layer to a build space which is surrounded, asappropriate, by container walls and applied to a build platform, and abinder is selectively printed thereon, using a print head, according tocomputer data. The particle area onto which the binder is printed stickstogether and solidifies under the influence of the binder and, ifnecessary, an additional hardener. The build platform is then lowered bya distance of one layer thickness into a build cylinder and providedwith a new layer of particulate material, which is also printed asdescribed above.

These steps are repeated until the desired height of the molding isachieved. A three-dimensional object is thus produced from the printedand solidified areas.

After it is completed, the molding produced from solidified particulatematerial is embedded in loose particulate material and is subsequentlyremoved therefrom. This is done, for example, using an extractor. Thisleaves the desired molding, from which the remaining adhering particlesare removed, for example by brushing.

Other powder-supported rapid prototyping processes work in an identicalor similar manner, for example, selective laser sintering or electronbeam sintering, in which a loose particulate material is also applied inlayers and selectively solidified with the aid of a controlled physicalradiation source. The aforementioned method is summarized under theterm, “three-dimensional printing” or “3D printing.”

However, the provision of a build container or build cylinder having abuild platform which may be lowered vertically into the build containerrequires a high degree of technical complexity for sealing the buildcontainer wall against the build platform to prevent uncontrolledoutflow of the particulate material through the gap between the buildplatform and the build container wall. Another disadvantage of alowerable build platform is the constantly increasing weight to be movedon the build platform as the building process progresses. In particularduring application of another layer, it may be necessary to lower thebuild platform by a distance of more than one layer thickness and thento raise it again to the dimension required in order to adjust the layerthickness with sufficient accuracy.

In a reversing operation of this type, not only does the entire weightof the power feedstock, including the build platform, need to beovercome but also the friction forces between the power bed and thebuild container wall. This results in high stresses on the guides anddrives of a vertically moving build platform, in particular in the caseof large build spaces and high feedstock densities.

In contrast, EP 1 872 928 A1 proposes to raise the discharging deviceand the print head relative to the build platform instead of loweringthe build platform relative to the discharging device and print head forbuilding larger three-dimensional moldings as the layering processprogresses. This publication furthermore proposes to construct solidwalls made of particulate material by solidifying the edge areas of theapplied particulate material and by forming, from these walls, a buildspace-delimiting build container in whose inner chamber moldings of aselective size and shape may be constructed. It is alternativelyproposed to construct moldings on the build space in a free-standingmanner without using a build container for encompassing and supportingpreviously applied layers. For this purpose, the discharging device isdesigned as a dosing device which may undergo controlled activation anddeactivation for the controlled output of a predetermined, preferablyconstant, linear volume flow of particulate material per length unit andper time unit, so that particulate material is not unnecessarily strewnaround the molding to be built or is not “emptied” prematurely and thusdoes not lose its function while the layer is being deposited. However,such dosing-controlled and “intelligent” discharging devices have arelatively complex structure and are correspondingly expensive.

“Unintelligent” discharging devices of a simpler design, on the otherhand, are unable to selectively dose particulate material or are notswitchable. For example, they include a scraper moving in the dischargedirection or a counter-rotating roller or an oscillating blade.

These devices then distribute a quantity of material in front of thedischarging device on the build space in the discharge direction. Theamount of particulate material then has to be sufficiently measuredbefore the discharging device travels over the build space.

Other design shapes may guide a quantity of material in two directionsaround the surface to be coated. These include discharging devices whichcomprise a simple, elongated hopper which has a slot on the underside asthe discharge opening for discharging particulate material. In anotherembodiment, at least one of the two hopper walls, for example, isreplaced by a counter-rotating roller.

In order for the process to progress as described, the dischargingdevice must pass completely over the area to be coated. However, adischarging device according to the aforementioned, simple and“unintelligent” design, loses a remaining quantity of material in frontof the discharging device in the discharge direction once the edge ofthe build space has been reached. This quantity of material would thenbe unavailable for the remaining building process. Nevertheless, itwould be desirable to return this lost material to the dischargingdevice for further layering.

A possibility for largely avoiding lost material is known, for example,from US 2005/0280185 A. In this publication, the quality of particulatematerial in the discharging device is predetermined by a sensor system.

The discharging device carries along a predetermined material quantitywhich is sufficient for coating the desired surface without producingtoo many waste particles after passing over the edge of the build space.In this case, however, the quantity must be very precisely determined toavoid too small a dosing in each cases, which would result ininsufficient layering. The continuous decrease in the quantity ofmaterial in the discharging device during travel has proven to beanother disadvantage of this method, resulting in an unsteady coatingprocess. This may cause the feedstock density to be greater at thebeginning of discharging device travel than at the end of the travel,due to the greater weight of the material, when a residual amount isleft over in the discharging device.

In contrast, the object of the invention is to refine a method and adevice of the aforementioned type in such a way that a variable andcoating material-saving adjustment of the build space size is possiblewhile simultaneously maintaining high coating quality, despite a simpleand cost-effective design of the discharging device.

SUMMARY OF THE INVENTION

The invention is based on the idea that no free-flowing material orparticulate material may flow out or be discharged through the dischargeopening of a non-switchable discharging device, i.e., an “unintelligent”discharging device which has no way to turn the material flow throughthe discharge opening on and off, when the discharge opening is closedby a body which is located on an appropriate level and over which thedischarging device passes.

A body of this type then simulates an already discharged layer offree-flowing material, which prevents further discharge of material whenthis layer reaches the same level as the discharge opening of thedischarging device. In this case, after all, the discharge opening hasalready been closed by the already discharged layer.

By designing the body or the build platform to be able to change atleast the vertical position of the body in relation to the buildplatform, the size of the build space may be easily limited by the bodywithout requiring a build container which is laboriously adjusted to theparticular size of the build space. When the discharging device with itsdischarge opening comes into contact with the surface of the body, whichis suitably placed on the edge of the build space in the verticaldirection, the body closes the discharge opening, whereby no morefree-flowing material is dischargeable at the edge of the build space.

Alternatively or additionally, the body is designed in such a way thatit does not close the discharge opening but instead has means such as anopening to be controllably opened or closed, for example, for thepurpose of discharging or conducting free-flowing material that is notused for layering from the discharge opening into a collectingcontainer, so that it may be fed back into the layering process.

According to the invention, it is therefore proposed that at least onebody delimiting the build space in at least one discharge direction ofthe discharging device and the build platform are vertically adjustablerelative to each other according to the particular progress with whichthe layer body is being constructed, in such a way that a surface of thebody facing the discharge opening is aligned flush with a topmost layerof the layer body which is yet to be produced or has already beenproduced, in order to close the discharge opening of discharging deviceand to prevent the discharging device from discharging free-flowingmaterial or to discharge free-flowing material not used for layeringinto a collecting container when the discharge opening is located abovethe body.

It is advantageous that, even when using an “unintelligent,”non-switchable, non-dosing and only displacement-controlled dischargingdevice, it is possible to discharge free-flowing material only withinthe build space delimited by the body and to avoid, in particular,discharging material in the area of the build platform located outsidethe build space. As a result, it is not necessary to remove residualmaterial located outside the build space, which has a positive effect onthe costs. The option of using an “unintelligent,” non-switchable,non-dosing and only displacement-controlled discharging device inconnection with the invention also helps lower costs because adischarging device of this type is much more cost-effective than an“intelligent” discharging device. An only displacement-controlled and“unintelligent” discharging device is understood to be a dischargingdevice which travels a certain computer-controlled discharge route, forexample from a starting position to a reversing position, and whichdischarges or permits the outflow of free-flowing material along thisdischarge route and through the always open discharge opening onto thebuild space. In particular, the discharging device does not have anymeans of closing the discharge opening or, for instance, dosing thequantity of free-flowing material to be discharged, depending on thetraveling distance.

Advantageous refinements of and improvements to the invention specifiedin the independent claims are made possible by the measures discussed inthe dependent claims.

It is particularly advantageous if the at least one body is designed tobe adjustable within a horizontal plane parallel to the build platformfor the purpose of variably delimiting the build space. The arealextension of the build space may then be delimited by the at least onebody, in particular if one body is disposed in one discharge directionof the discharging device (e.g., the X direction) and another body isdisplayed in a discharge direction perpendicular thereto (e.g., the Ydirection) in order to achieve a delimited build space in bothdirections.

This ensures that a discharge of free-flowing material beyond the edgesof the build space no longer occurs in both directions.

As mentioned above, the discharging device is preferably an“unintelligent” discharging device and only displacement-controlled withregard to a predefined discharge distance extending from a startingposition at one edge of the build space to a reversing position at theopposite edge of the build space. This additionally lowers costs.

The reversing position may be predefined by the particular position ofthe at least one body, and the starting position is stationary. In thiscase, the coating operation is started from a stationary startingposition, and the reversing position is defined as a function of theposition of the at least one body on the horizontal plane.

Conversely, however, the starting position may be predefined by theparticular position of the at least one body, and the reversing positionis stationary. In this case, the coating operation is started from theat least one body and its direction is reversed at the stationaryreversing position. In both cases, the length of the discharge route tobe traveled by the discharging device and thus the extension of thebuild space in this direction depends on the position of the at leastone body.

The starting position of the discharging device, i.e., the place fromwhich the discharging operation is started, is particularly preferably afilling position in which the discharging device may be filled orrefilled with free-flowing material by means of a filling device.Depending on whether the starting position is or is not dependent on theposition of the at least one body, the position of the filling device ona horizontal plane parallel to the build platform is therefore alsodependent on the position of the body. The filling device is thenpositioned, for example, above the discharging device.

The container for collecting excess material is disposed, for example,at the reversing position or at the starting position. One body may thenbe disposed at the starting position and at least one other body may bedisposed at the reversing position, means being provided in the one bodyor in the other body for introducing free-flowing material into thecollecting container or for conducting it thereto. The one body closingthe discharge opening of the discharging device is then used to preventa discharge of free-flowing material at the edge of the build space,while the purpose of the other body on the opposite edge of the buildspace is to introduce excess, i.e., unused, free-flowing material intothe collecting container, so that it may be supplied for reuse in thelayering process.

The at least one body is preferably a flat, plate-shaped body, forexample a metal plate with or without a through-opening, depending onwhether it is to prevent a discharge from the discharge opening of thedischarging device or whether it is to discharge material into thecollecting container.

It is therefore particularly preferable to design the build platform tobe adjustable vertically relative to the body and discharging device andto design the body and the discharging device to be adjustablehorizontally relative to the build platform, in order to flexibly adaptthe build space to the particularly requirements and, in particular, tothe particular molding to be constructed, while minimizing the loss offree-flowing material.

The invention additionally relates to a method for constructing a layerbody from a plurality of superimposed layers of free-flowing material ona build platform within a build space.

Additional measures which improve the invention are illustrated ingreater detail below together with the description of one exemplaryembodiment of the invention on the basis of the drawing.

BRIEF DESCRIPTION OF THE DRAWING

Exemplary embodiments of the invention are illustrated below in thedrawing and explained in greater detail in the following description. Inthe drawing,

FIG. 1 shows a top view of a device for producing moldings withdifferent build space sizes on a build platform.

FIGS. 2a through 2d show a schematic cross-sectional view of a devicefor producing moldings according to one preferred embodiment of theinvention.

FIGS. 3a through 3g show a schematic cross-sectional view of anotherembodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a preferred embodiment of a device 13 for constructing alayer body 5 from a plurality of superimposed layers of, for example,powdered, initially loose, particulate material on a build platform 6within a build space 11 a through 11 d.

Build spaces 11 a through 11 d of different sizes illustrated in FIG. 1extend over a wide area in FIG. 1 parallel to build platform 6 in thehorizontal X and Y directions, layer body 5 being constructed in thevertical Z direction, which is perpendicular to the drawing plane inFIG. 1.

Device 13 comprises a discharging device 1 which is movable back andforth over build space 11 a through 11 d in at least one dischargedirection, in this case, for example, in the X direction and/or the Ydirection, discharging device 1 having at least one discharge opening14, which is not visible in this view and from which the particulatematerial may be discharged in individual superimposed layers during themovement of discharging device 1.

Discharging device 1 is preferably a non-switchable discharging device,i.e., without the option of turning the material flow through dischargeopening 14 on and off, so that free-flowing material or particulatematerial may or may not flow out. Instead, particulate materialcontinuously flows through discharge opening 14 in discharging device 1unless discharge opening 14 is closed by means belonging to dischargingdevice 1 or if no (more) particulate material is present in a reservoirof discharging device 1.

Device 13 furthermore comprises a print head 2 which is moveable backand forth over build space 11, for example, in the X and Y directionsfor the selective application of binder onto at least one dischargedlayer in order to solidify and join together discharged layers inlocally predetermined areas of build space 11 a through 11 d by theaction of binders, so that at least one molding 4 is formed by thesolidified and joined areas of the layers of layer body 5 in a knownmanner.

Alternatively, print head 2 could be replaced with a radiation source ifthe discharged, free-flowing material already contains a binder which isthen hardened by selective irradiation with the radiation source for thepurpose of creating molding 4. Or the free-flowing material itself isfused or slightly melted by the irradiation and joined thereby.

The extension of build space 11 a through 11 d in the X and Y directionsis predefined by the application of material to build platform 6,different sizes of build spaces 11 a through 11 d being illustrated inFIG. 1. If build space 11 a through 11 d is described in the illustratedorthogonal coordinate system 9, each extension or size of build spaces11 a through 11 d may be displayed as a rectangle, starting from origin10. The dimensions of build platform 6 in the X and Y directions thencorrespond to a maximum displayable size of one build space 11 a.

One rectangular side of a build space 11 of this type is generallydetermined, for example, by the discharge route or discharge travel ofdischarging device 1 in discharge direction X, so that, in the presentcase, the size of the build space is dependent on the length of thisdischarge route. Based on the example in FIG. 1, the discharge route ofdischarging device 1 thus increases from 11 d to 11 a in the Xdirection.

The other rectangular side of a build space 11 a through 11 d isdetermined, for example, by the width of discharge opening 14 ofdischarging device 1 in the Y direction, which may be formed, inparticular, by an elongated slot. In the present case, different lengthsof discharge openings 14 of discharging device 1 are provided to obtainthe variable-length rectangular side of build spaces 11 a through 11 din the Y direction. In the present case, therefore, one layer of layerbody 5 may, on the whole, be completely produced in one pass of thedischarge route in the X direction.

Only one rectangular side of a build field 11 is visible in thecross-sectional side representation in FIGS. 2a through 2d and 3athrough 3g . In these illustrations, the edges of build space 11 arepreferably formed by printed walls 3 in the X and Y directions, i.e.,the particulate material is selectively solidified here by print head 2so that loose particulate material of layer body 5 located within theedges of build space 11 is not able to flow off in areas outside buildspace 11. For this purpose, print head 2 suitably prints the edge areasof each discharged layer. Alternatively, however, a separate buildcontainer or separate build walls could be used to delimit build space11.

In the embodiments illustrated herein, build platform 6 is preferablylowered as the height of layer body 5 increases in the Z direction, inparticular using drives and guides which are not illustrated.Discharging device 1 therefore remains on its initial level for each newlayer to be discharged and is therefore movable relative to buildplatform 6, for example only in the X direction and/or the Y direction.Alternatively, build platform 6 could be designed to be stationary, andat least discharging device 1 could be designed to be movable relativeto stationary build platform 6 in both the X and Y directions as well asthe Z direction.

In the specific embodiments in FIGS. 2a through 2d and 3a through 3g ,build platform 6 is vertically adjustable relative to, for example, twobodies 8, 8 a delimiting the build space in discharge direction X of thedischarging device according to the particular progression ofconstruction, in such a way that surfaces of bodies 8, 8 a facingdischarge opening 14 of discharging device 1 are aligned flush with atopmost layer of layer body 5 yet to be produced or already produced.

The purpose of the two bodies 8, 8 a is to close discharge opening 14 ofdischarging device 1 and to prevent discharging device 1 fromdischarging free-flowing material (body 8) or to discharge free-flowingmaterial that is not used for layering into a collecting container 7(body 8 a) when discharge opening 14 of discharging device 1 is locatedabove particular body 8, 8 a.

At least one of bodies 8, 8 a, in this case preferably body 8, isdesigned to be adjustable within a horizontal plane parallel to buildplatform 6 and, in particular, in the X direction, for the purpose ofvariably delimiting build space 11. The areal extension of build space11 is then delimited by body 8 at least in the X direction, inparticular when the position of body 8 is designed to be movable indischarge direction X of discharging device 1.

Build platform 6 is therefore particularly preferably designed to beadjustable relative to bodies 8, 8 a, discharging device 1 and printhead 2 in the vertical Z direction, and body 8, discharging device 1 andprint head 2 are designed to be movable relative to build platform 6 inthe horizontal X direction. The position of body 8 is adjusted in the Xdirection in order to flexibly adapt build space 11 to the particularrequirements and, in particular, to the one or more moldings 4 to beconstructed, while minimizing losses of free-flowing material.

The two bodies 8, 8 a are consequently always on the same level in the Zdirection, in particular through attachment to or guidance on astationary frame of device 13, which is not illustrated herein, whilebuild platform 6 is being lowered as the construction of layer body 5continues to progress.

Bodies 8, 8 a are preferably flat, plate-shaped bodies, for examplemetal plates with and without through-openings 12, depending on whetherthe particular body 8 or 8 a is to prevent material from beingdischarged from discharge opening 14 of discharging device 1 or topermit or cause material to be discharged into collecting container 7.Body 8 a is therefore preferably formed by a perforated plate having atleast one through-opening 12. Body 8 a may furthermore also comprisemeans for conducting particulate material into collecting container 7.Not least, at least one through-opening 12 of body 8 a may becontrollable, i.e., the at least one through-opening 12 may be opened orclosed as a function of external electrical, pneumatic and/or mechanicalcontrol signals in order to discharge or conduct free-flowing materialnot used for layering from discharge opening 14 into collectingcontainer 7 for the purpose of returning it to the layering process.

As indicated above, discharging device 1 is displacement-controlled, forexample, by an electronic control unit, which is not illustrated here,with regard to a predefined discharge route in the X direction,extending from an initial, starting or idle position 14 at one edge ofbuild space 11 to a reversing position 16 at the opposite edge of buildspace 11; i.e., in response to a starting command, it first moves fromits starting or idle position 14 in the X direction to reversingposition 16, at which the direction of movement is automaticallyreversed, if necessary upon expiry of a certain dwell time at reversingposition 16.

During the movement of discharging device 1 along the discharge route,which simultaneously forms the length of the rectangular side of buildspace 11 visible herein, particulate material is preferably continuouslyapplied to build platform 6 or to a previously layered part of layerbody 5 via discharge opening 14.

Prior to this, discharging device 1, which in this case is, for example,a discharging hopper of a filling device which is not illustrated hereinbut is easy to picture, is preferably filled with a quantity ofparticulate material corresponding to a multiple of layers to beapplied.

According to the embodiment in FIGS. 2a through 2d , starting position15 is predefined by the position of body 8 adjustable in the Xdirection, while reversing position 16, at which body 8 a is located, isstationary. In this case, the coating operation is started from theparticular set position of body 8, body 8 closing discharge opening 14of discharging device 1 precisely at starting position 15 and preventingparticulate material from being discharged, as is easily pictured on thebasis of FIG. 2a . Only after discharging device 1 has moved a distancefrom body 8 is free space the height or thickness of one layer providedbelow discharge opening 14, into which particulate material may bedischarged to form a single layer. Specifically, the following methodsteps are carried out in the embodiment in FIGS. 2a through 2 d:

Build platform 6 is first positioned in the vertical direction relativeto bodies 8 and 8 a, to discharging device 1 and to print head 2, insuch a way that the surfaces of body 8, 8 a facing discharge opening 14,discharge opening 14 of discharging device 1 and print head 2 aredisposed higher than the current topmost layer of layer body 5 by adistance of one layer thickness.

When discharging device 1 is located in its starting position rightabove body 8, its discharge opening 14 is closed by body 8, as is easilypictured on the basis of FIG. 2a . Print head 2 is then preferablylocated on the far side of opposite reversing position 16 of dischargingdevice 1, i.e., outside build space 11, in order to avoid collidinglater on with discharging device 1 once it has reached reversingposition 16.

At the same time or thereafter, discharging device 1 is filled withfree-flowing material at starting position 15 in a quantity sufficientto produce, for example, a single layer of layer body 5. The fillingdevice, which is not illustrated herein, is then positioned, forexample, above discharging device 1.

The control unit then activates discharging device 1 so that it movesfrom starting position 15 to reversing position 16 while dischargingparticulate material to construct one layer. This situation isillustrated in FIG. 2 a.

When discharging device 1 has reached body 8 a at reversing position 16,discharge opening 14 is located right above opened through-opening 12 inbody 8 a, so that any excess particulate material still remaining indischarging device 1 for producing a layer is able to flow intocollecting container 7, which is disposed, for example, belowthrough-opening 12 in body 8 a. The control unit then returns emptieddischarging device 1 to its starting position 15, whereby it is followedby print head 2 in order to provide or print binder onto a locallypredetermined area of the discharged layer. Since discharging device 1is empty during this movement, i.e., it is moved without particulatematerial, an unwanted application of particulate material to layer body5 is avoided. This operation is illustrated in FIG. 2 c.

Once discharging device 1 has reached starting position 15, it isrefilled with particulate material for one layer, and the describedcycle begins all over again (FIG. 2d ). The cycle according to FIGS. 2athrough 2d are repeated until the entire layer body 5 is created. Printhead 2 also prints the areas that represent walls 3 of layer body 5.

In the specific embodiment illustrated in FIGS. 3a through 3g , incontrast to the specific embodiment in FIGS. 2a through 2d , reversingposition 16 is determined by the position of body 8 set in the Xdirection, and starting position 15, where body 8 a is located, isstationary. In this case, the coating operation is started at astationary starting position 15, and reversing position 16 is defineddepending on the position of body 8 in the X direction.

Specifically, the following method steps are carried out in theembodiment in FIGS. 3a through 3 g:

Build platform 6 is first positioned vertically (in the Z direction)relative to bodies 8, 8 a, to discharging device 1 and to print head 2,in such a way that, on the one hand, the surfaces of body 8, 8 a facingdischarge opening 14 and, on the other hand, discharge opening 14 aredisposed higher than the current topmost layer of layer body 5 by adistance of one layer thickness. Body 8 a, which has the at least onethrough-opening 12, and collecting container 7 located thereunder arepositioned at starting position 15, and body 8, which does not have athrough-opening 12 of this type, is positioned at reversing position 16.

To prevent particulate material from flowing through through-opening 12in body 8 a into collecting container 7 in starting position 15,discharging device 1 is filled by a filling device, which is notillustrated herein, for example in a position located a short distancefrom starting position 15 in the X direction, in which a part of body 8a facing build space 11 is able to close discharge opening 14 indischarging device 1, as shown in FIG. 3g . Discharging device 1 isfilled with particulate material for producing, for example, two layersof layer body 5.

Print head 2 is located in the starting position, preferable on the nearside of body 8 a, so that it does not collide with discharging device 1.Discharging device 1 is then activated by the control unit in order tomove from starting position 15 to reversing position 16 for the purposeof discharging particulate material in this matter to construct a layer(FIG. 3a ). Once reversing position 16 at the edge of build space 11 hasbeen reached, body 8 closes discharge opening 14 in discharging device1. Print head 2 is subsequently activated by the control unit in orderto print binder onto a locally determined area of the discharged layeras well as the areas that form walls 3 of layer body 5 (FIG. 3b ).Afterwards, print head 2 returns to its starting position.

Once a layer has been discharged and selectively printed, build platform6 is lowered by a distance of one layer height or one layer thickness sothat the surfaces of bodies 8 and 8 a facing discharge opening 14,discharge opening 14 of discharging device 1 and print head 2 are againdisposed higher than the current topmost layer of layer body 5 by adistance of one layer thickness.

Discharging device 1 is then activated by the control unit in order tomove from reversing position 16 back to starting position 15 whiledischarging particulate material for constructing another layer, asillustrated in FIG. 3 c.

After starting position 15 is reached, any particulate material that isnot used for the two discharged layers may flow through the at least onethrough-opening 12 of body 8 a into collecting container 7 (FIG. 3d ).

Print head 2 is subsequently activated so that it prints binder onto theareas of molding 4 and walls 3 of the additional discharged layer.Emptied discharging device 1 may then move in front of print head 2, asshown in FIG. 3 e.

According to FIG. 3f , discharging device 1 and print head 2 are movedback to their starting position 15 after the printing operation, buildplatform 6 preferably being simultaneously lowered by a distance of onelayer height or one layer thickness for the purpose of making space inthe vertical direction for a subsequent layering operation.

After discharging device 1 has been refilled with particulate materialin the position according to FIG. 3g , the described cycle begins allover again and is repeated until complete layer body 5 is created.Finally, loose particulate material is removed from the layer body inthe unprinted areas, leaving molding 4 behind.

Instead of lowering build platform 6 vertically relative to bodies 8, 8a, to discharging device 1 and to print head 2 as the constructioncontinues to progress, bodies 8, 8 a, discharging device 1 and the printhead could, of course, also be designed to be movable relative to astationary build platform 6 in the vertical Z direction, according toanother embodiment.

LIST OF REFERENCE NUMERALS

-   -   1 Discharging device    -   2 Print head    -   3 Printed wall    -   4 Molding    -   5 Loose particulate material    -   6 Build platform    -   7 Collecting container    -   8 Body    -   8 a Body    -   9 Coordinate system    -   10 Coordinate origin    -   11 Build space    -   12 Through-opening    -   13 Device    -   14 Discharge opening    -   15 Starting position    -   16 Reversing position

What is claimed is:
 1. A method comprising: the steps of i. constructinga first article from a plurality of superimposed layers of afree-flowing material, on a build platform within a first build space,the layers being solidified and joined together in locally predeterminedareas, including: applying the free-flowing material from a dischargedevice in layers, and selectively joining the free-flowing material;wherein the discharge device moves back and forth over the first buildspace; wherein the build platform is stationary and the discharge deviceis movable with respect to the stationary build platform; adjusting theheight of the discharge device relative to the stationary buildplatform; and forming one or more outer walls for defining the firstbuild space so that loose free-flowing material within the first buildspace is prevented from flowing off into areas outside of the firstbuild space; wherein the one or more outer walls are printed walls ofthe free-flowing material being solidified and joined together;  whereinthe first article is formed by the solidified and joined areas of thelayers within the first build space; and ii. following the constructingof the first article, repeating (i) for constructing a second article ina second build space, wherein the first build space and the second buildspace are different build spaces over the build platform.
 2. The methodof claim 1, wherein the action of a binder solidifies and joins togetherthe free-flowing material in the locally predetermined areas.
 3. Themethod of claim 2, wherein the first article is embedded in loosefree-flowing material and the method includes a step of removing thefirst article from the loose free-flowing material.
 4. The method ofclaim 3, wherein the first article is removed with an extractor prior tostep of constructing the second article.
 5. The method of claim 3,wherein the binder is applied by a print head.
 6. The method of claim 5,wherein the discharge device and the print head both move in the samedirection during the step of applying the binder.
 7. The method of claim6, wherein the discharge device applies the free-flowing particulatematerial at a time when the print head is not applying binder.
 8. Themethod of claim 7, wherein the print head applies the binder at a timewhen the discharge device is not applying the free-flowing material. 9.The method of claim 8, wherein the free-flowing material is a powderparticulate material and the build space is a variable build space forreducing waste of power particulate material.
 10. The method of claim 1,wherein fusing solidifies and joins together the layers of thefree-flowing material in the locally predetermined areas.
 11. The methodof claim 1, wherein the method includes a step of irradiating thefree-flowing material to solidify and join together the layers of thefree-flowing material in the locally predetermined areas.
 12. The methodof claim 1, wherein the one or more outer walls surround the buildspace.
 13. A method comprising the steps of: i. constructing at leastone first article from a plurality of superimposed layers offree-flowing material, on a build platform within a first build space,the layers being solidified and joined together in locally predeterminedareas by the action of a binder, including: applying the free-flowingmaterial from a discharge device in layers, and applying the binder froma print head; wherein the discharge device and the print head move backand forth over the first build space; wherein the build platform isstationary and the discharge device and the print head are movable withrespect to the stationary build platform; the discharge device appliesthe free-flowing material at a time when the print head is not applyingbinder; and the print head applies the binder at a time when thedischarge device is not applying the free-flowing material;juxtapositioning the discharge device with an uppermost layer of thefree-flowing material; and forming an outer wall at an edge of the firstbuild space, the outer wall defining the first build space so that loosefree-flowing material within the first build space is prevented fromflowing off into areas outside of the first build space; wherein theouter wall is a printed wall of the free-flowing material beingsolidified and joined together by the action of the binder;  wherein theat least one first article is formed by the solidified and joined areasof the layers within the first build space; and ii. following theconstructing of the at least one first article, repeating (i) forconstructing at least one second article in a second build space,wherein the first build space and the second build space are differentbuild spaces over the build platform; wherein a layer is completed inone pass of the discharge device over the build space.
 14. The method ofclaim 13, wherein the build space is variable for reducing waste of thefree-flowing material.
 15. The method of claim 14, wherein the step ofapplying the free-flowing particulate material and the binder includesmoving the print head and the discharge device together in a firstdirection; and then moving the print head and the discharge devicetogether in a second direction opposite the first direction.
 16. Themethod of claim 13, wherein the discharge device includes has anelongated shape for applying a layer of the free-flowing material in asingle pass of the discharge device over the build space.
 17. The methodof claim 13, wherein the first build space is enclosed by one or moreprinted walls including the outer wall, wherein the one or more printedwalls enclosing the first build space are generally vertical and free ofsupport by a solid support structure outside of the first build space.18. A method comprising the steps of: i. constructing at least one firstarticle from a plurality of superimposed layers of free-flowingparticulate material, on a build platform within a first build space,the layers being solidified and joined together in locally predeterminedareas by the action of a radiation source, including: applying thefree-flowing particulate material from a discharge device in layers, andapplying radiation from a radiation source; wherein the discharge deviceand the radiation source move back and forth over the first build space;wherein the build platform is stationary and the discharge device ismovable with respect to the stationary build platform; adjusting theheight of the discharge device relative to the stationary buildplatform; juxtapositioning the discharge device with an uppermost layerof the free-flowing particulate material; and forming an outer wall atan edge of the first build space, the outer wall defining the buildspace so that loose free-flowing particulate material within the firstbuild space is prevented from flowing off into areas outside of thefirst build space; wherein the outer wall is a printed wall of thefree-flowing particulate material being solidified and joined togetherby the action of the radiation source;  wherein the at least one firstarticle is formed by the solidified and joined areas of the layerswithin the first build space; and ii. following the constructing of theat least one first article, repeating (i) for constructing at least onesecond article in a second build space, wherein the first build spaceand the second build space are different build spaces over the buildplatform.
 19. The method of claim 18, wherein the radiation sourceselectively irradiates the free-flowing particulate material for fusinglayers of the free-flowing particulate material.
 20. The method of claim18, wherein the free-flowing particulate material includes a binder andthe radiation source selectively solidifies and joins the layers by theaction of the irradiation of the binder.
 21. The method of claim 18,wherein the first article is embedded in the loose free-flowingparticulate material and the method includes a step of extracting thefirst article from loose free-flowing particulate material.
 22. Themethod of claim 18, wherein the discharge device has an elongated shapefor applying a layer of the free-flowing material in a single pass ofthe discharge device over the build space.